[Devel] [PATCH RHEL7 COMMIT] ms/dcache: don't need rcu in shrink_dentry_list()

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.18.2.vz7.14.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.18.2.vz7.14.8
------>
commit 8998fd28c3d40840b1cc4319a30c83f3003216fe
Author: Miklos Szeredi <mszeredi at suse.cz>
Date:   Fri May 27 12:53:10 2016 +0400

    ms/dcache: don't need rcu in shrink_dentry_list()
    
    Since now the shrink list is private and nobody can free the dentry while
    it is on the shrink list, we can remove RCU protection from this.
    
    Signed-off-by: Miklos Szeredi <mszeredi at suse.cz>
    Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
    (cherry picked from commit 60942f2f235ce7b817166cdf355eed729094834d)
    Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 fs/dcache.c | 27 ++++-----------------------
 1 file changed, 4 insertions(+), 23 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 1961048..c584d23 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -826,23 +826,9 @@ static void shrink_dentry_list(struct list_head *list)
 {
 	struct dentry *dentry, *parent;
 
-	rcu_read_lock();
-	for (;;) {
-		dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
-		if (&dentry->d_lru == list)
-			break; /* empty */
-
-		/*
-		 * Get the dentry lock, and re-verify that the dentry is
-		 * this on the shrinking list. If it is, we know that
-		 * DCACHE_SHRINK_LIST and DCACHE_LRU_LIST are set.
-		 */
+	while (!list_empty(list)) {
+		dentry = list_entry(list->prev, struct dentry, d_lru);
 		spin_lock(&dentry->d_lock);
-		if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
-			spin_unlock(&dentry->d_lock);
-			continue;
-		}
-
 		/*
 		 * The dispose list is isolated and dentries are not accounted
 		 * to the LRU here, so we can simply remove it from the list
@@ -858,23 +844,20 @@ static void shrink_dentry_list(struct list_head *list)
 			spin_unlock(&dentry->d_lock);
 			continue;
 		}
-		rcu_read_unlock();
 
 		parent = dentry_kill(dentry, 0);
 		/*
 		 * If dentry_kill returns NULL, we have nothing more to do.
 		 */
-		if (!parent) {
-			rcu_read_lock();
+		if (!parent)
 			continue;
-		}
+
 		if (unlikely(parent == dentry)) {
 			/*
 			 * trylocks have failed and d_lock has been held the
 			 * whole time, so it could not have been added to any
 			 * other lists. Just add it back to the shrink list.
 			 */
-			rcu_read_lock();
 			d_shrink_add(dentry, list);
 			spin_unlock(&dentry->d_lock);
 			continue;
@@ -888,9 +871,7 @@ static void shrink_dentry_list(struct list_head *list)
 		dentry = parent;
 		while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
 			dentry = dentry_kill(dentry, 1);
-		rcu_read_lock();
 	}
-	rcu_read_unlock();
 }
 
 static enum lru_status dentry_lru_isolate(struct list_head *item,